This invention relates to dithiocarbamyl carboxylic acids and their use as multifunctional additives for lubricating oils.
Zinc dialkyldithiophosphates (ZDDPs) have been used as anti-fatigue, anti-wear, extreme pressure and friction modifying additives for lubricating oils for many years. However, they are subject to several drawbacks owing to their zinc and phosphorus contents. During operation of an internal combustion engine, lubricating oil enters the combustion chambers by means such as clinging to cylinder walls as the piston makes its down stroke. When phosphorus-containing lubricating oil compositions enter the combustion reaction, phosphorus enters the exhaust stream where it acts as a catalyst poison thus shortening the useful life of the catalytic converter. In addition, the presence of zinc contributes to the emission of particulates in the exhaust.
In view of the aforementioned shortcomings with the known zinc and phosphorus-containing additives, efforts have been made to provide lubricating oil additives which contain neither zinc nor phosphorus. Illustrative of non-zinc (i.e., ashless), non-phosphorus-containing lubricating oil additives are the reaction products of 2,5-dimercapto-1,3,4-thiadiazole and unsaturated mono-, di- and tri-glycerides of U.S. Pat. No. 5,512,190 and the dialkyl dithiocarbamate-derived organic ethers of U.S. Pat. No. 5,514,189.